This invention relates to a specific combination of two different polyolefin clarifying and nucleating agents, namely bis-3,4-dimethyldibenzylidene sorbitol and bis-p-methyldibenzylidene sorbitol. Such a combination surprisingly provides improved clarification and crystallization temperatures to polypropylene articles and formulations, better than bis-p-methyldibenzylidene sorbitol alone and equivalent or better than 3,4-dimethyldibenzylidene sorbitol alone. Such a combination of compounds thus permits the utilization of a new additive for the purpose of modifying polyolefin properties, such as polypropylene clarification and nucleation. The inventive combination may be introduced within any polyolefin composition, again preferably polypropylene, which may then be molded into any shape or form. A method of producing a polyolefin plastic utilizing the inventive combination of compounds is also provided.
Dibenzylidene sorbitol acetals (xe2x80x9cDBSxe2x80x9d), substituted DBS, such as can be made with alkyl substituted aromatic aldehydes, and related acetals have found utility as nucleating agents, clarifying agents, gelling agents, processing aids, and strength modifiers in polyolefin resins, polyester resins, deodorant, and antiperspirant compositions; hydrocarbon fuels; waste liquids, especially those containing organic impurities; and paint.
Such compounds are utilized to provide nucleation sites for polyolefin crystal growth during cooling of a molten formulation. Without being limited to one specific scientific theory, it is believed that DBS compounds form fibrous networks within the molten polyolefin (such as polypropylene) at a temperature well above that required for polyolefin crystal formation. The fibrous networks appear to act as sites for more ordered and faster polyolefin crystallization during cooling. During the process of crystallization, polymer crystals organize into larger superstructures which are referred to as spherulites. The more uniform, and preferably smaller, the spherulite size, the reduced possibility for light to be scattered. In such a manner, optical opacity of the polyolefin article itself can be controlled. Thus, DBS compounds are very important to the polyolefin industry in order to provide such desired nucleation and clarification properties.
DBS derivative compounds are typically prepared by the condensation reaction of two moles of an aromatic aldehyde with one mole of a polyhydric alcohol, such as xylitol or sorbitol. Examples of suitable processes may be found in Murai et al., U.S. Pat. No. 3,721,682; Murai et al., U.S. Pat. No. 4,429,140; Machell, U.S. Pat. No. 4,562,265; Kobayashi et al., U.S. Pat. No. 4,902,807; and Scrivens et al., U.S. Pat. No. 5,731,474. All of these references are hereby incorporated by reference in their entirety.
Specific clarifying and nucleating agents for polyolefins include bis-3,4-dimethyldibenzylidene sorbitol (3,4-DMDBS) and bis-p-methyldibenzylidene sorbitol (MDBS). These specific compounds and polyolefins containing such compounds have been taught previously in U.S. Pat. No. 4,371,645 to Mahaffey and U.S. Pat. No. 5,049,605 to Rekers, respectively. Such compounds are thus individually well known as polyolefin additives and exhibit excellent low haze measurements within polyolefins (as low as about 8.0% for 3,4-DMDBS and about 10% for MDBS in random polypropylene copolymer injection molded 50 mil thick plaques having 2000 ppm of clarifier added).
However, there are drawbacks from utilizing MDBS as a clarifying agent since degradation of such a compound into the benzaldehyde and sorbitol components creates a problem with migration of such benzaldehydes from the target polyolefin. In such a situation, foul odors and tastes are generated such that the target polyolefin is limited in its end-use function to non-food contact applications. To combat this, Milliken and Company developed 3,4-DMDBS. Such a compound appears to suffer from the same type of degradation possibilities; however, the resultant benzaldehyde, being 3,4-dimethyl substituted, does not create the same organoleptic problems as its p-methylbenzaldehyde counterpart. As a result, 3,4-DMDBS has become the primary clarifying agent throughout the polyolefin market.
Unfortunately, though, 3,4-DMDBS is relatively expensive to manufacture. The manufacturing costs required to produce 3,4-DMDBS are above those for MDBS. As a result, there remains a great desire to develop a more cost-effective, yet acceptable clarifying agent or composition for polyolefins which exhibits similar haze results as either of the two compounds individually. To date, there has been no teaching or fair suggestion for any such improvements to lower the amount of 3,4-DMDBS in order to reduce the costs of such a composition solely comprising such a polyolefin clarifying agent without sacrificing clarification ability. There does exist a combination of 3,4-DMDBS with bis(p-chlorobenzylidene) sorbitol in Japanese Application Hei 8[1996]-199003 to Kobayashi; however, such a composition provides deleterious results from an organoleptic perspective. Japanese Application Hei 8[1996]-32415, also to Kobayashi, teaches a combination of MDBS with bis-p-chlorodibenzylidene sorbitol as a polyolefin additive as well. Again, organoleptics are problematic with such a composition. Neither teaching shows or fairly suggests the combination of 3,4-DMDBS and MDBS. The only other teachings concerning such polyolefin clarifying compounds have been as individually utilized compounds within polyolefin compositions and articles, as noted above. Thus, there remains a desire to provide a more cost-effective but similarly performing clarifying agent comprising the excellent clarifier 3,4-DMDBS.
Therefore, an object of the invention is to provide a lower cost alternative to a polyolefin clarifier containing 3,4-DMDBS alone exhibiting excellent clarifying capabilities for the same polyolefin articles and compositions. Another object of the invention is to provide a polyolefin composition or article exhibiting a haze measurement of below 10% comprising a clarifying combination of 3,4-DMDBS and MDBS.
Accordingly, this invention encompasses a polyolefin additive composition comprising a combination of both bis(3,4-dimethylbenzylidene) sorbitol and bis(4-methylbenzylidene) sorbitol. More specifically, this invention encompasses such a combination consisting of from 5 to 95% by weight of the total combination of bis(3,4-dimethylbenzylidene) sorbitol and from 5 to 95% by weight of the total combination of bis(4-methylbenzylidene) sorbitol. Finished solid articles of polyolefins, such as, preferably, though not necessarily, polypropylene, comprising such an additive composition are also contemplated within this invention. Furthermore, such an invention is also defined and thus encompasses a polyolefin nucleator composition comprising at least 1000 ppm of a mixture of compounds, wherein said compounds are bis(3,4-dimethylbenzylidene) sorbitol and bis(p-methylbenzylidene) sorbitol, wherein said polyolefin nucleator composition provides a crystallization onset temperature within a target polyolefin article formulation above the crystallization onset temperature provided for a comparative polyolefin article comprising the same polyolefin formulation but comprising bis(p-methylbenzylidene) sorbitol as its sole polyolefin nucleator component, wherein the concentration of said sole polyolefin nucleator component within said comparative polyolefin article is equivalent to the total concentration of the polyolefin nucleator mixture within said target polyolefin article. Also contemplated is a polyolefin nucleator composition comprising at least 1000 ppm of a combination of compounds, wherein said compounds are bis(3,4-dimethylbenzylidene) sorbitol and bis(p-methylbenzylidene) sorbitol, wherein said polyolefin nucleator composition provides a peak crystallization temperature within a target polyolefin article formulation above the peak crystallization temperature provided for a comparative polyolefin article comprising the same polyolefin formulation but comprising bis(p-methylbenzylidene) sorbitol as its sole polyolefin nucleator component, wherein the concentration of said sole polyolefin nucleator component within said comparative polyolefin article is equivalent to the total concentration of the polyolefin nucleator mixture within said target polyolefin article. Further contemplated is a polyolefin clarifier composition comprising at least 1000 ppm of a combination of nucleator compounds, wherein said compounds are bis(3,4-dimethylbenzylidene) sorbitol and bis(p-methylbenzylidene) sorbitol, wherein said polyolefin clarifier composition provides a haze measurement within a target polyolefin article formulation below the haze measurement provided for a comparative polyolefin article comprising the same polyolefin formulation but comprising bis(p-methylbenzylidene) sorbitol as its sole polyolefin clarifier component, wherein such haze measurements are made in accordance with ASTM Standard Test Method D1003-61, and wherein the concentration of said sole polyolefin nucleator component within said comparative polyolefin article is equivalent to the total concentration of the polyolefin nucleator mixture within said target polyolefin article. The importance of and definitions of such crystallization onset temperatures, peak crystallization temperatures, and haze measurements are discussed in greater detail below. Lastly, the invention encompasses a method of nucleating a polyolefin comprising the steps of (a) providing a nucleator composition comprising at least 1000 ppm of a combination of bis(3,4-dimethylbenzylidene) sorbitol and bis(4-methylbenzylidene) sorbitol; (b) providing a polyolefin formulation; (c) mixing said composition of step xe2x80x9caxe2x80x9d with the polyolefin of step xe2x80x9cbxe2x80x9d; (d) melting said resultant mixture of step xe2x80x9ccxe2x80x9d; and allowing said molten mixture of step xe2x80x9cdxe2x80x9d to cool. Nowhere within the pertinent prior art is such a combination, polyolefin additive composition, polyolefin articles comprising such combinations and additives compositions, or methods of producing polyolefin articles taught or fairly suggested.
The invention thus comprises basically both 3,4-DMDBS and MDBS in specific proportions. The combination of both compounds has been avoided in the past, as noted above, due to the difficulties in utilizing MDBS in a large range of applications and end-uses. Without the apparent ability to provide an acceptable clarifier composition including such a compound, the possibility of servicing only a limited market of end-users has thwarted widespread attempts of incorporating such a compound within different clarifying formulations. Without the desire or need to investigate the effects of such an inventive combination of compounds within a polyolefin clarifying formulation, production and analyses of such potential mixtures have been deemphasized.
However, with the need to provide lower cost alternatives to 3,4-DMDBS alone, as well as the availability of certain types of compounds to prevent MDBS degradation, neutralize degrading acids and other oxidants, and/or compounds which scavenge free degraded benzaldehyde, all within the target polyolefin, the potential for avoiding the aforementioned difficulties with organoleptic issues may potentially permit more widespread use of MDBS within a broader market of end-uses, particularly non-food contact applications. Such potential organoleptic improvements for MDBS containing polyolefins is rather limited, however, since the necessity of scavenging large amounts of degraded benzaldehydes requires the presence of an appreciable amount of extra solids within the target polyolefin itself. Such an addition is problematic since the increase in solids within the target polyolefin invariably affects the clarity and cost of the target formulation. Thus, polyolefins comprising all MDBS are still problematic on a widespread basis due to the difficulties in reducing haze and organoleptic problems simultaneously with such clarifying compounds. Hence, the development of the inventive combination of 3,4-DMDBS and MDBS as a synergistically active clarifying agent is of great importance within the clarified polyolefin industry.
As noted above, surprisingly, it has now been found that such a mixture of clarifiers exhibits a synergistic clarifying effect in polyolefin. As noted in TABLE 2, below, for random copolymer (RCP), for example, about 2000 ppm of 3,4-DMDBS provides a haze measurement of about 8% and MDBS at 2000 ppm of about 10% (all within, as one example, 50 mil plaques of injection molded RCP). By mixing the two compounds, for example, to about 1500 ppm 3,4-DMDBS and about 500 ppm MDBS, the resultant haze measurement is about 8.4% (much lower than for MDBS alone). Furthermore, a mixture of about 1600 ppm MDBS with about 400 ppm 3,4-DMDBS provides a haze measurement of about 7.9%. Thus, even though MDBS exhibits an appreciably higher haze measurement than 3,4-DMDBS, surprisingly the combination of the two different compounds provides a comparable haze result for 3,4-DMDBS alone.
Such a result is against commonly accepted practice. For example, as noted above, and without intending to be bound to any specific scientific theory, it appears that the DBS compound within a polyolefin appears to provide a fibrous network of nucleation sites for polyolefin crystal growth during cooling of the molten polymer. The network formed by 3,4-DMDBS alone accords what appears to be standard small spherulite sizes for low haze measurements. The network formed by MDBS produces larger average spherulite sizes, thereby producing high haze measurements. It is noted that all haze measurements noted herein include a standard deviation of +/xe2x88x920.25 haze units.
Although haze is an important measurement to determine the effectiveness of certain clarifying agents, other characteristics exhibited by such agents, and transferred to the final polyolefin product are of great interest as well. For instance, crystallization is important in order to determine the time needed to form a solid from the molten polyolefin/DBS composition. The rate of crystallization is typically quantified by reporting the onset crystallization temperature, which defines the beginning of the crystallization process, and the peak crystallization temperature, which defines the temperature where the crystallization rate is highest. Both the onset crystallization temperature and the peak crystallization temperature are indicative of the crystallization process occurring in a polymer sample. In order to reduce the amount of time needed to form the final product, as well as to provide the most effective nucleation for the polyolefin, the best DBS compounds added will most likely, though not necessarily, also provide the highest peak crystallization temperature and the highest onset crystallization temperature.
The crystallization temperature exhibited by 3,4-DMDBS in RCP, for example, is greater than an entire degree above that for MDBS in RCP (114.1xc2x0 C. to 112.9xc2x0 C.). Thus, without intending to be bound to any specific scientific theory, it appears that the polypropylene crystals form more readily and quickly with 3,4-DMDBS due to the higher crystallization temperature exhibited thereby. However, (in the mixed systems) the addition of amounts of 3,4-DMDBS appear not only not to reduce the haze results from MDBS alone, but also increase both the peak crystallization and onset crystallization temperatures. It would be expected that the arrangement of polyolefin crystals would be more haphazard with a mixed clarifier system since the fibrous networks formed by the initial 3,4-DMDBS would seemingly produce different spherulite size crystals of polyolefin than would the MDBS network. Again, this appears not to be the case in this instance. The similarity in haze results to 3,4-DMDBS alone suggests that the polyolefin crystal growth remains uniform in effect. Such results are, again, highly unexpected in view of common understandings of nucleated and clarified polyolefins.
A similar phenomenom occurs with regard to the aforementioned crystallization onset temperatures. MDBS exhibits, in RCP, a crystallization onset temperature of about 117.1xc2x0 C. at 2000 ppm, and 3,4-DMDBS exhibits, also in RCP at 2000 ppm, a crystallization onset temperature of about 118.6xc2x0 C. With a combination of these two additives, the crystallization onset temperature is increased, surprisingly, to a level as high as almost 119xc2x0 C. All crystallization and onset temperatures listed herein include a statistical error of +/xe2x88x920.1xc2x0 C.
Thus, it has been found that a composition of from 5-95% by weight of MDBS and from 5-95% by weight of 3,4-DMDBS, with a total of 100% for both components, provides the highly unexpected benefits as noted above, particularly when incorporated within a target polyolefin, preferably polypropylene. Preferably, such a mixture is from about 10-90% by weight MDBS and from about 10-90% by weight of 3,4-DMDBS; more preferably, about 20-90% by weight of MDBS and from about 10-80% by weight of 3,4-DMDBS; still more preferably, 25-90% MDBS, and 10-75% 3,4-DMDBS, and most preferably about 50-80% MDBS and about 20-50% 3,4-DMDBS. Such a combination may be incorporated within an additives package composition including other components, including, base polyolefin, and other compounds and formulations noted below in greater detail. Such an inventive combination, and compositions comprising such an inventive combination, may be present in any type of standard polyolefin additive form, including, without limitation, powder, prill, agglomerate, liquid suspension, and the like. Basically, any form may be exhibited by such a combination or composition including such combination made from blending, agglomeration, compaction, and/or extrusion. The total concentration of the inventive combination of nucleator compounds within the target polyolefin may be anywhere from about 1000 ppm to about 4000 ppm; preferably such a concentration is from about 1000 ppm to about 3500 ppm; more preferably is from about 1200 ppm to about 3000 ppm; still more preferably is from about 1500 ppm to about 3000 ppm; and most preferably from about 1500 ppm to about 2200 ppm.
Optional additives within the base composition comprising this inventive mixture may include plasticizers, antistatic agents, stabilizers, ultraviolet absorbers, and other similar standard polyolefin thermoplastic additives. Other additives may also be present within this composition, most notably antioxidants, antistatic compounds, perfumes, acid neutralizers, and the like. In particular, it is contemplated that certain organoleptic improvement additives be added for the purpose of permitting increased amounts of MDBS to be incorporated within the inventive combination, compositions thereof, and end-product polyolefin comprising such. The term xe2x80x9corganoleptic improvement additivexe2x80x9d is intended to encompass such compounds and formulations as antioxidants (to prevent degradation of both the polyolefin and possibly the target MDBS and/or 3,4-DMDBS), acid neutralizers (to prevent the ability of appreciable amounts of residual acids from attacking the DBS compounds), and benzaldehyde scavengers (such as hydrazides, hydrazines, and the like, to prevent the migration of foul tasting and smelling benzaldehydes to the target polyolefin surface). Such compounds and formulations can be added in any amounts in order to provide such organoleptic improvements as needed. However, the amounts should not appreciably affect the haze results for the target polyolefin itself. Thus, lower amounts on the order of from about 20 ppm to about 2,000 ppm of the total polyolefin component are desired.
The term polyolefin or polyolefin resin is intended to encompass any materials comprised of at least one polyolefin compound. Preferred examples include polypropylene, polyethylene, polybutylene, and any blends or copolymers thereof, whether high or low density in composition. The term thermoplastic is well known in the art to mean a polymeric material which will melt upon exposure to sufficient heat but will retain its solidified state, but not prior shape (without use of a mold), upon sufficient cooling. The nucleated polyolefin is intended to be utilized as, for instance and not by limitation, medical devices, such as syringes, intravenous supply containers, and blood collection apparati; pipes and tubes; standard storage containers; food packages; liquid containers, such as for drinks, medicines, shampoos, and the like; apparel cases; microwaveable articles; shelves; cabinet doors; mechanical parts; automobile parts; and any article where the effects of nucleation may be advantageous.
The inventive nucleator and/or clarifier compositions are also defined in terms of their ability to provide improved crystallization onset temperatures, peak crystallization temperatures, and haze measurements within polyolefin article formulations above such quantifiable properties available through the sole utilization of bis(p-methylbenzylidene) sorbitol as a nucleator and/or clarifier within the same polyolefin article formulation and at the same total concentration as the inventive nucleator combination, as noted above. The term xe2x80x9csame polyolefin article formulationxe2x80x9d in this context intended to define the same base polyolefin content as used to produce the comparable polyolefin articles with the inventive compositions incorporated therein, including the same manufacturing process parameters (e.g., melting temperatures, molder barrel temperatures, cooling rates and temperatures, and the like). It would be well appreciated by the ordinarily skilled artisan that such a term does not connote the same exact polyolefin article itself. Thus, in comparison with standard polyolefin article formulations of the same base poyolefin content but with bis(p-methylbenzylidene) sorbitol as the sole nucleating/clarifying additive, the inventive compositions provide increased crystallization onset temperatures and peak crystallization temperatures and decreased haze measurements where the concentration of the sole polyolefin nucleator component a comparative polyolefin article is equivalent to the total concentration of the polyolefin nucleator mixture within the inventive target polyolefin article.